1. Technical Field of the Invention
The present invention relates to a micropump for the nebulization of fluids with enhanced metering valve. A micropump of this kind is suitable for mounting on a cap for glass or plastic bottles destined to contain perfumes or other substances which, according to their specific use, require nebulization.
2. Prior Art
Generally, this type of micropump comprises a pump body and a set of hollow stem and piston such as to constitute together with the body a "metering chamber". The exit duct for the fluid includes the longitudinal cavity of the hollow stem, a so called "compression pre-chamber" obtained in a dispensing push-button and at least a passage from this "compression pre-chamber" to a "vortex chamber" of a nebulization element fitted with related orifice. The stem and piston set is movable within the body thanks to the antagonistic action between the dispensing push-button and a helical spring, abutting in the "metering chamber" against the front end of the stem. The stem and the piston of the set are, themselves, mutually movable to uncover one or more through holes in the stem, at the moment the dispensing push-button is pressed to allow the fluid to be nebulized to pass from the "metering chamber" into the fluid exit duct.
In a system of this type the pressure inside the "metering chamber" necessary to obtain a correct nebulization is guaranteed by a valve, which could be called "minimum pressure" valve, obtained with the aforesaid piston and a "pre-loading" spring abutted between the piston and a flange provided on the stem inside the pump body. Such "minimum pressure" valve determines the threshold pressure which must exist in the "metering chamber" for the through holes of the stem to be uncovered, and the pressurized fluid to travel through the longitudinal cavity of the stem to reach the "compression pre-chamber", and accelerated and exited from the orifice of the nebulization element, creating the nebulization cone.
In the prior art system the correct nebulization requires the fluid to reach the "compression pre-chamber" with sufficient pressure to be accelerated adequately. This depends mainly on the head losses the fluid undergoes in its exit duct. The smaller the head losses, with the threshold pressure being equal, the more pressure the fluid maintains in correspondence with the "compression pre-chamber". Since the "minimum pressure" valve, comprised by the piston which covers and, vice versa, uncovers the holes by means of the "pre-loading" spring, is situated away from the "compression pre-chamber", the head losses, i.e. those along the hollow stem, are significant, and hence pressure in the "compression pre-chamber" can be insufficient.
Pump systems already exist which use micro-springs associated to micro-shutters positioned inside the cylindrical duct of the stem in the vicinity of the nebulization element, which acting on small sections, maximize, other conditions being equal, the dispensing pressure value. Such systems, however, are particularly complex and, given their small size, the production of their components and their assembly, especially in terms of dimensional precision and repeatability, are very onerous, and thus entail an increase of the final cost of the pumps and of the containers whereto they are applied.